The invention relates to a method for the shift sequence control of a continuously variable automatic transmission, especially of a motor vehicle, having gear-stage switchover. The transmission ratio of the automatic transmission is continuously adjustable within a set gear stage by means of an adjusting unit.
Continuous automatic transmissions having gear-stage switchover are already known under the designation xe2x80x9cCVT-transmissionxe2x80x9d. This relates to combination transmissions for motor vehicles which have a stepped automatic (planetary sets) and a continuously adjustable unit for continuously adjusting the transmission ratio within a particular adjusted gear stage (range).
The known methods for shift sequence control are unfortunately not suited to ensure a satisfactory adjustment of the transmission ratio on such a combination transmission (CVT-transmission having range switchover).
The method of the invention is characterized in that a coordinated, data-dependent control of the gear stage switchover and the continuous transmission ratio adjustment takes place by means of a common shift sequence control system. The control of the gear-stage switchover as well as of the continuous transmission ratio adjustment is coordinated within an adjusted gear stage (range) by means of a common shift sequence control system. For this reason, it is possible to achieve adjustment actions of a transmission ratio on a continuously variable automatic transmission flexibly by means of suitable data changes. A coordinated, data-dependent control of this kind thereby permits a correct shift or adjustment of a transmission ratio on a corresponding continuous automatic transmission. This shift or adjustment of a transmission ratio is satisfactory with respect to the operation of a vehicle. A corresponding control by means of a higher-ranking shift sequence control system can be realized in a relatively simple manner while applying a suitable control program (software).
An initialization of the adjusting unit, which is configured especially as a hydrostatic unit, takes place with advantage. Here, the subject matter is a hydraulic continuously variable transmission. By initializing the adjusting unit, it is possible, in the context of a zero-point adaptation, to compensate possibly present tolerances and/or position discrepancies of components operatively connected to the adjusting unit. This ensures a precise continuous adjustment of a transmission ratio on a continuously variable transmission by means of the adjusting unit.
Advantageously, the initialization takes place in the form of a particular zero-point adaptation of the adjusting unit with reference to a forward travel and/or rearward travel of the vehicle. The adjusting unit has an operating position starting with which a reverse travel of the vehicle is possible, even though the planetary sets are configured for a forward travel. Here, one must distinguish between two separate, specific operating positions of the adjusting unit, namely, a first operating position starting with which a rearward travel of the motor vehicle is possible but not wanted and a second operating position, wherein a forward travel of the vehicle is possible and wanted. These two operating positions of the adjusting unit can shift because of deterioration of the adjusting unit and/or because of deterioration of components operatively connected to the adjusting unit. In this way, inaccuracies are compensated by means of the particular zero-point adaptation of the adjusting unit with respect to a forward travel and rearward travel of the motor vehicle in a reliable manner. These inaccuracies are unwanted and go back to the particular positioning of the adjusting unit.
According to a preferred embodiment, the initialization takes place before a particular taking into service of the motor vehicle. Because of the limited time span available for carrying out a correct initialization, a relatively rapidly and precisely acting control is required, which can be ensured with the use of a higher-ranking shift sequence control system for the coordinated and data-dependent control of the gear stage switchover and of the continuous transmission ratio adjustment.
With advantage, the adjusting unit is adjusted by means of a step motor for the continuous adjustment of the transmission ratio. The step motor is operatively connected to the shift sequence control system. A step motor can be controlled in a relatively simple manner and is suited especially for the displacement of the adjusting unit provided for the continuously changeable transmission ratio and configured especially as a hydrostatic unit. If present, occurring discrepancies between a particular step motor position and a corresponding operating position of the adjusting unit (hydrostatic unit) can be compensated by means of the above-mentioned initialization of the adjusting unit. Likewise, and in the same manner, discrepancies between the desired and actual positions of the step motor can be compensated. These discrepancies are, for example, caused by electronic tolerances, fluctuations in a hydraulic pressure system or the like. Since the drive of the step motor is integrated especially during a gear stage switchover in a phase control of the shift sequence control, it is possible to trigger a step motor action in each shifting phase.
Advantageously, the shift sequence control system determines an assumption of a defined shift position of the adjusting unit in advance of enabling a gear stage switchover. In this way, it is ensured that the adjusting unit is, during a gear stage switchover (range change), in a defined shift position in which synchronism for the adjustment of gears in the automatic transmission is present. These gears are represented by corresponding planetary sets.
In accordance with a preferred embodiment, a position control of the adjusting unit takes place in the context of the continuous transmission ratio adjustment. By means of a position control of this kind, it is advantageously possible to compensate possibly present discrepancies between a particular input value for a step motor position, which is to be adjusted, and a corresponding position of the adjusting unit (hydrostatic unit). A model of characteristic values or characteristic fields or of mechanical or hydraulic basic information can be applied in the context of a position control to compensate for unwanted transmission ratio deviations.
Preferably, for position control, the following adjusting parameters are applied:
corrective step number per computation step;
output frequency of the corrective steps in a defined time span.
In this way, the transmission ratio can be influenced favorably with respect to operation by means of the position control.
Further advantageous embodiments of the invention are evident from the description.